While I can’t speak from experience, I’m pretty sure that a person getting hit by a train/bus/car/etc is unlikely to result in a blood explosion, as if the victim were an overfilled water balloon primed to coat bystanders with viscera upon impact. I get that hyperbole is a thing and bloodying a bystander is a handy visualization of the trauma they incurred from witnessing a terrible accident, but come on, actors get paid to act. They can do traumatized just fine without PAs whipping ketchup at them. If you’re making a silly and/or highly stylized movie, by all means, paint the town red. If you’re not, don’t. Pass it on.